1. Field of the Invention
The present invention relates to a gear actuator for engaging/disengaging gears of a transmission, in particular, in AMT systems (automatic manual transmission).
2. Description of the Related Art
In so-called automatic manual transmissions (AMT), the gears of the transmission are engaged by means of an electro-hydraulic actuator. The actuator for a transmission with an xe2x80x9cHxe2x80x9d shifting pattern is configured of several pistons and corresponding mechanisms in order to carry out a gear shifting movement and/or a gutter movement.
Such a gear actuator is known, for example, from DE 199 31 973 A1. In this connection, a complexly configured unit comprised of actuating devices, sensors, and valve devices is proposed in order to engage and disengage a gear of the transmission.
In FIG. 8 a different known gear actuator 1 as well as a gutter actuator 19 are illustrated. As illustrated in FIG. 8, the actuator comprises two working pistons 3 and 5 as well as two bushings 23 or two auxiliary pistons which are supplied with a controlled system pressure via pressure control valves EVG1 and EVG2, respectively, in order to move a selector shaft 9. The position of the piston elements 3, 5 as well as that of the bushings 23 or the auxiliary pistons is determined by a complex control of the pressure control valves EVG1 and EVG2. Such a gear actuator requires a complex mechanical configuration and has a plurality of components. In order to be able to determine the respective position of the selector shaft 9, a sensor is provided. This results in an increased manufacturing expenditure and a highly branched hydraulic line system for this known gear actuator. Moreover, a complex control must be provided in order to control the valves of the pistons.
It is therefore an object of the present invention to provide a gear actuator for engaging and disengaging gears in a transmission which enables a safe and reliable engagement and disengagement of gears while providing a simple configuration and easy, inexpensive manufacture.
This object is solved by a gear actuator comprising a first working piston surface, a second working piston surface, an auxiliary piston, and a pressure control valve which controls the pressure for the second working piston surface, wherein the first working piston surface and the pressure valve are supplied with a system pressure, and wherein the first working piston surface and the pressure control valve can be decoupled from the system pressure by a shut-off valve. Advantageous embodiments are the subject matter of the dependent claims.
The gear actuator according to the invention for engaging and disengaging gears in an automatic manual transmission, in particular, in an AMT system, comprises a first working piston surface, a second working piston surface, an auxiliary piston, and a pressure control valve. The pressure control valve controls the pressure for the second working piston surface. The first working piston surface and the pressure control valve are supplied with a system pressure. In this connection, the first working piston surface and the pressure control valve can be decoupled from the system pressure by a shut-off valve. According to the invention, the system pressure is to be understood as a pressure which is provided for operating a hydraulic system. With the design of the gear actuator according to the invention, the actuator can be configured simpler and with fewer components in comparison to the prior art. According to the invention, precisely only one auxiliary piston is required and, moreover, precisely only one pressure control valve is required which controls the process of gear engagement and gear disengagement. The shut-off valve ensures in this connection that, while a gear is engaged, no forces can be transmitted onto the transmission through the gear actuator because the shut-off valve separates the gear actuator from the system pressure. This increases the service life of the transmission. Moreover, by separating the hydraulic connection from the gear actuator, leakage can be minimized so that the service life of the motor and the hydraulic pump can be extended.
According to a preferred embodiment of the invention, the first working piston surface is provided on a first working piston and the second working piston surface is provided on a second working piston. Accordingly, the gear actuator has two working pistons which can be arranged on opposite sides of a selector shaft of the transmission.
According to another preferred configuration of the present invention, the first working piston surface and the second working piston surface are provided on a common working piston. This means that the common working piston is a double-action piston. This further reduces the number of components, and, in particular, the costs and the weight of the gear actuator can be reduced further.
Preferably, the pressure control valve controls the pressure for the auxiliary piston. In this way, the second working piston surface and the auxiliary piston are supplied commonly with controlled system pressure by means of the pressure control valve. In this connection, the second working piston surface and the auxiliary piston are loaded with the same controlled system pressure.
According to a further preferred embodiment of the present invention, the auxiliary piston is supplied via the shut-off valve with system pressure. Accordingly, the first working piston surface and the auxiliary piston are supplied with system pressure. Accordingly, the pressure level at the first working piston surface and at the auxiliary piston corresponds to the pressure level of the system pressure which acts uncontrolled on the components.
In order to determine a neutral position of the selector shaft in the transmission, the auxiliary piston is configured as a stop for the selector shaft. Accordingly, the neutral position, in which no gear is engaged, can be determined in a simple and reliable way. In the neutral position, the transmission can perform a gutter change when a gear is to be shifted which is arranged in a different gutter of the transmission.
Preferably, the first and the second working piston surfaces are differently sized. In this way, the forces which effect the movement of the gear actuator can be adjusted with minimal control expenditure. Particularly preferred in this connection is a configuration wherein the first working piston surface is smaller than the second working piston surface.
According to a further preferred embodiment of the present invention, the pressure control valve controls the pressure level of the system pressure in three ranges. In this connection, in a first range a gear of a gutter of the transmission is engaged, in a second range the neutral position is determined, and in a third range another gear of the same gutter is engaged. This means that, when the first and the second gear are arranged, for example, in one gutter of the transmission, a movement in the direction of the first gear is possible in the first pressure range, and a movement in the direction of the second gear is possible in the third pressure range. In this connection, the system pressure is controlled preferably to 0% to 40% of the system pressure within the first range. In the second range (neutral position), the system pressure is controlled preferably to 41% to 59% of the system pressure; after reaching the neutral position, no movement occurs. In the third range, the system pressure is preferably controlled to 60% to 100% of the system pressure.
Advantageously, the shut-off valve for interrupting the system pressure supply to the gear actuator is configured at the same time as a clutch valve which supplies also a clutch cylinder and a gutter actuator with system pressure. Accordingly, the shut-off valve performs simultaneously also other functions so that the number of components can be further reduced.
According to the invention, in particular, the neutral position of the gear actuator can be determined as a function of the state of the pressure control valve. In this connection, the neutral position can always be determined without employing a sensor. Moreover, the two end positions of the gear actuator can be determined also. However, in order to be able to move in a defined way into intermediate positions of the gear actuator, for example, a synchronization point, a sensor can be preferably provided for determining the position. A slow shifting of the gears is however also possible without sensor because, according to the invention, the neutral position is found always without a sensor. In this way, a gutter selection is also possible when sensor failure occurs.